1. Field of the Invention
Embodiments of the present invention relate to a boost control apparatus mounted, for example, on a vehicle or the like.
2. Description of the Related Art
On an electric vehicle, such as an electric car, a hybrid car, and a fuel cell vehicle, an inverter is mounted in order to control a motor generator that generates driving force used for running and regenerative power used for power storage. Since electric power used by the inverter varies depending on a running state or the like, a voltage conversion apparatus (or a converter) is provided between a power storage apparatus and the inverter in some cases.
In order to improve fuel efficiency of the electric vehicle, it is effective to reduce a loss of the converter. Thus, for example, in Japanese Patent Application Laid Open No. 2011-120329, there is proposed a technology in which a boost converter is switching-driven only by a one-side element (hereinafter referred to as “one-side element control”). According to the one-side element control, it is considered that the loss of the converter can be reduced, for example, due to a reduction in current ripple.
In Japanese Patent Application Laid Open No. 2005-151606, there is proposed a technology related to control of the converter in which a moment at which current that flows through a reactor becomes nearly zero (or zero crossing) is detected.
In the one-side element control, a relation between output current and a duty ratio significantly changes before and after the zero crossing, and it is thus preferable to change control content depending on whether or not it is the zero crossing. In other words, it is preferable to switch between control for a zero-crossing region and control for a non-zero-crossing region, and to perform either one, as occasion demands.
Here, the zero crossing can be determined, for example, by monitoring the current that flows through the reactor and applied voltage or the like; however, it is not easy to detect the zero crossing with high accuracy and without delay in conventional technologies including the aforementioned patent literatures. If the timing of the zero crossing cannot be accurately detected, duty control cannot be appropriately switched, which can result in such a technical problem that desired output current cannot be obtained. In particular, it is considered that such a problem frequently occurs in a high-frequency state.